Tunable acoustical absorbing composite batt

ABSTRACT

A composite batt structure that forms an effective low frequency sound absorber for use in buildings, appliances, automotive vehicles, and the like. The composite structure uses a facer covering a batt comprised of carded and crosslapped mixture of fibers. The general acoustic behavior of the composite batt structure has a low frequency absorption maximum by varying the number of crosslaps or the proportions of the fiber mixture. This allows for the composite batt structure to be tunable or layered with different laps.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates generally to an acoustic absorber for use anyplace where low frequency sound needs to be minimized, that isessentially sound transparent in the voice frequency range, and a methodfor tuning the acoustical absorbance.

2. Description of the Related Art

An acoustic absorber is known that comprises a batt and facer structure.For instance, United States Patent Application Publication 2009/0173569to Levit et al discloses an acoustic absorber with a core ofacoustically absorbing material having two major surfaces, and a facingfor covering the core on at least one major surface. However, there isno disclosure to means to tune the acoustic absorber.

It is desirable to have an acoustic absorber that is tunable to absorbvarious acoustic frequencies.

SUMMARY OF THE INVENTION

An embodiment of the invention is a tunable acoustically absorbingarticle comprising a batt of acoustically absorbing material comprisedof 10 to 70% by weight staple flash spun plexifilamentary fibers orstaple melt spun fibrillated fibers, 10 to 70% by weight staple fibers,5 to 30% by weight binding agent, which are carded and crosslapped; anda facer adhered to the batt on at least one major surface.

Another embodiment of the present invention is changing the number ofcrosslaps in the batt of acoustically absorbing material to tune thefrequency at which the acoustically absorbing article attenuates soundto a desired frequency.

Definitions

The term “batt” as used herein means single or multiple sheets of fibersused in the production of a nonwoven.

The term “nonwoven” or “web” as used herein means a structure ofindividual fibers or threads that are positioned in a random manner toform a planar material without an identifiable pattern, as in a knittedfabric.

The term “plexifilamentary fibers” as used herein means athree-dimensional integral network or web of a multitude of thin,ribbon-like, film-fibril elements of random length and with a mean filmthickness of less than about 4 microns and a median fibril width of lessthan about 25 microns. The average film-fibril cross sectional area ifmathematically converted to a circular area would yield an effectivediameter between about 1 micron and 25 microns. In plexifilamentarystructures, the film-fibril elements intermittently unite and separateat irregular intervals in various places throughout the length, widthand thickness of the structure to form a continuous three-dimensionalnetwork.

The term “polymer” as used herein, generally includes but is not limitedto, homopolymers, copolymers (such as for example, block, graft, randomand alternating copolymers), terpolymers, etc., and blends andmodifications thereof. Furthermore, unless otherwise specificallylimited, the term “polymer” shall include all possible geometricalconfigurations of the material. These configurations include, but arenot limited to isotactic, syndiotactic, and random symmetries.

The term “polyolefin” as used herein, is intended to mean any of aseries of largely saturated polymeric hydrocarbons composed only ofcarbon and hydrogen. Typical polyolefins include, but are not limitedto, polyethylene, polypropylene, polymethylpentene, and variouscombinations of the monomers ethylene, propylene, and methylpentene.

The term “polyethylene” as used herein is intended to encompass not onlyhomopolymers of ethylene, but also copolymers wherein at least 85% ofthe recurring units are ethylene units such as copolymers of ethyleneand alpha-olefins. Preferred polyethylenes include low-densitypolyethylene, linear low-density polyethylene, and linear high-densitypolyethylene. A preferred linear high-density polyethylene has an upperlimit melting range of about 130° C. to 140° C., a density in the rangeof about 0.941 to 0.980 gram per cubic centimeter, and a melt index (asdefined by ASTM D-1238-57T Condition E) of between 0.1 and 100, andpreferably less than 4.

The term “polypropylene” as used herein is intended to embrace not onlyhomopolymers of propylene but also copolymers where at least 85% of therecurring units are propylene units. Preferred polypropylene polymersinclude isotactic polypropylene and syndiotactic polypropylene.

The term “facer” as used herein means any solid film, such aspolyethylene, or any nonwoven fabric that is adhered to the face of abatt.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting the acoustic absorption vs. % by weight ofstaple flash spun plexifilamentary fibers for various crosslappings.

FIG. 2 is a graph depicting the acoustic absorption vs. crosslappings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a tunable acoustically absorbingarticle comprising a batt of acoustically absorbing material having 10to 70% by weight of staple flash spun plexifilamentary fibers or staplemelt spun fibrillated fibers, and 10 to 70% by weight of staple fibers,and 5 to 30% by weight binding agent; which are carded and crosslapped;and subsequently faced with a facer on at least one surface. Preferably,the present invention is directed to a tunable acoustically absorbingarticle comprising a batt of acoustically absorbing material 25 to 60%by weight of staple flash spun plexifilamentary fibers or staple meltspun fibrillated fibers, and 25 to 60% by weight of staple fibers, and 5to 30% by weight binding agent; which are carded and crosslapped; andsubsequently faced with a facer on at least one surface.

The tunable acoustically absorbing article comprises two elements. Thefirst element is a batt of acoustically absorbing material whichcomprises a carded and crosslapped structure made from staple flash spunplexifilamentary fibers or staple melt spun fibrillated fibers, staplefibers, and binding agent.

The staple flash spun plexifilamentary fibers of the tunableacoustically absorbing article can be made according to the flashspinning process described in U.S. Pat. No. 7,744,989 to Marin et al.,which is hereby incorporated by reference. The flash spinning processproduces a flash spun web of plexifilamentary fibers. Theplexifilamentary fibers can be unbonded or lightly bonded. The flashspun web of plexifilamentary fibers can then be cut to a length of atleast about 2.5 cm to make the staple flash spun plexifilamentaryfibers. The staple flash spun plexifilamentary fibers preferably have asurface area of at most 10 m2/g, or a crush value of at least 1 mm/g,and more preferably a surface area of at most 5 m2/g, or a crush valueof at least 1.5 mm/g. The staple flash spun plexifilamentary fibers canbe made of polyolefin polymer, preferably polyethylene.

The staple melt spun fibrillated fibers can be made according to anygeneral process known to those skilled in the art. For example, meltspun fibrillated fibers can be made by melt spinning bicomponent polymerfibers with fiber cross sections such as round pie shape with pie wedgesof alternating polymers or islands in the sea with the islands made fromone polymer and the sea made from another polymer. The melt spunbicomponent polymer fibers can then be cut to a length of at least about2.5 cm to make staple melt spun unfibrillated fibers. The staple meltspun unfibrillated fibers are later converted into staple melt spunfibrillated fibers via a carding process. The staple melt spunfibrillated fibers can be made of polyolefin polymer, polyester polymer,polyamide polymer or mixtures thereof.

It has been found that the frequency at which the acoustic absorber ofthe present invention attenuates sound can be tuned by the proportion ofstaple melt spun fibrillated fibers in the batt. As shown in FIG. 1,higher proportion of staple melt spun fibrillated fibers absorb lowerfrequencies of sound. One embodiment of the present invention ischanging the proportion of staple melt spun fibrillated fibers in thebatt to tune the frequency at which the acoustic absorber attenuatessound to a desired frequency of sound.

The staple fibers can be made according to any general process known tothose skilled in the art. The staple fibers preferably are stiff toprovide some support and loft to the batt. The staple fibers can be madeof polyester polymer, preferably polyethylene terephthalate, polyolefinpolymer, polyamide polymer or viscose rayon.

The binding agent comprises at least one polymeric component with amelting point below the melting point of the staple flash spunplexifilamentary fiber melting point and the staple fiber melting point.The binding agent can take the form of staple binder fibers or smallparticles. The staple binder fibers can comprise multiple polymericcomponents with (a) at least one polymeric component with a meltingpoint below the melting point of the staple flash spun plexifilamentaryfiber melting point or the staple melt spun fibrillated fiber meltingpoint and the staple fiber melting point and occupying at least aportion of a surface of the staple binder fibers and (b) at least onepolymeric component with a melting point above that of the melting pointof the at least one polymeric component with a melting point below themelting point of the staple flash spun plexifilamentary fiber meltingpoint or the staple melt spun fibrillated fiber melting point and thestaple fiber melting point. A common example of this type of staplebinder fiber is a bicomponent fiber wherein a low melting point polymeron at least a portion of the surface of the fiber melts and adheres toanother fiber while a high melting point polymer does not melt keeping aportion of the fiber intact. The staple flash spun plexifilamentaryfibers or staple melt spun unfibrillated fibers, staple fibers and abinding agent are mixed and fed to a carding machine to form a cardedweb. The carding process splits the larger diameter staple flash spunplexifilamentary fibers into microfibers or splits the staple melt spununfibrillated fibers into staple melt spun fibrillated fibers bybreaking the fibers apart along the interfacial boundary between thedifferent polymers.

The carded web is fed, for example, onto a conveyor belt or apron to acrosslapper, where lapper aprons crosslap the carded web by traversing acarrier means such as an intermediate apron in a reciprocating motion,to produce a batt of fibers that are oriented primarily in thetransverse direction. The number of laps used to form the batt dependsupon variables such as the desired weight of the base layer, and thefinal weight of the batt. The batt is then, optionally, fed into an ovenat a temperature that will activate the binding agent to adhere fiberstogether and impart strength to the batt.

The staple flash spun plexifilamentary fibers or staple melt spununfibrillated fibers, staple fibers and a binding agent may optionallybe mixed and pre-opened in a card opener (For example a Dell'orcoVillani co/1500 machine.) The blend may then be fed through a chutefeeder (such as disclosed in U.S. Pat. No. 3,981,047), garnet (withcrosslapping), or air-lay equipment to make a batt. The batt may thenoptionally be fed into an oven at a temperature that will activate thebinding agent to adhere fibers together and impart strength to the batt.

It has been found that the frequency at which the acoustic absorber ofthe present invention attenuates sound can be tuned by the number ofcrosslaps in the batt. As shown in FIG. 2, higher crosslaps will absorblower frequencies of sound. Another embodiment of the present inventionis changing the number of crosslaps in the batt to tune the frequency atwhich the acoustic absorber attenuates sound to a desired frequency ofsound.

The second element is a facer. The facer element may be any solid film,such as polyethylene, or any nonwoven fabric. A preferred facer is amoisture vapor permeable, substantially liquid impermeable,substantially air impermeable nonwoven comprising flash spunplexifilamentary fibers. A suitable example is Tyvek® Homewrap™.

The tunable acoustically absorbing article is formed by covering onesurface of the batt with the facer. The tunable acoustically absorbingarticle does not require the facer to be fastened or adhered to thebatt. Optionally, the batt and facer may be fastened or adhered togetherfor convenience of handling. For example, the batt and the facer can beadhered together by a spray-on adhesive. Any suitable adhesive thatadheres the batt material to the facer material may be used.

Test Methods

In the non-limiting Examples that follow, the following test methodswere employed to determine various reported characteristics andproperties. ASTM refers to the American Society of Testing Materials.

Basis Weight was determined according to ASTM D-3776 and reported ing/m2. Thickness was obtained using a Gustin Bacon Measure-Matic™thickness tester with a 130.7 g. weight. Bulk Density was calculated bydividing the basis weight by the sample thickness. The number isreported in g/m3.

The acoustical composite materials of the present invention were testedfor absorption using a Model # 4206 impedance tube available from Bruel& Kjaer. The test procedures in accordance with ASTM E1050 and ISO 10534were followed. The absorption coefficient was recorded and graphed.Surface Area of the plexifilamentary fiber was measured by the BETnitrogen absorption method of S. Brunauer, P. H. Emmett and E. Teller,J. Am. Chem. Soc., V. 60 p 309-319 (1938) and is reported as m2/g. CrushValue was determined using the following procedure. Threeplexifilamentary fiber strands of different sizes were manually pulledfrom an unbonded plexifilamentary web. The three samples weighed aboutone, two and three grams. The reported crush values are the averages ofthe values measured on the three samples. Each sample plexifilamentarystrand was formed into a ball shape with minimum application of pressureto avoid crushing and the sample was then weighed in grams. A crushtester comprised of an acrylic sample holder and crusher was used tomeasure the crush value of each sample. The sample holder comprised acylindrical section having an inner diameter of 2.22 inches (5.64 cm)and an outer diameter of 2.72 inches (6.91 cm). The center of thecylinder was located at the geometric center of a square base measuring6.00 inches by 6.00 inches (15.24 cm by 15.24 cm). The crusher compriseda cylindrical plunger rod (diameter =0.75 inches (1.91 cm)) having afirst disk-shaped face (the disk having a thickness of 0.25 inches (0.64cm) and a diameter of 2.20 inches (5.59 cm)) located at one end of theplunger rod and a second disk on the plunger rod spaced back 1.50 inches(3.81 cm) from the first disk.

The second disk also had a thickness of 0.25 inches (0.64 cm) and adiameter of 2.20 inches (5.59 cm). The disks were sized slightly smallerthan the inner diameter of the cylindrical sample holder in order toallow air to escape from the sample during crushing. Theplexifilamentary samples were placed, one at a time, in the sampleholder and a thin piece of paper having a diameter of about 2.2 inches(5.59 cm) was placed on top of the plexifilamentary sample prior tocrushing. The plunger rod was then inserted into the cylindrical sampleholder such that the first disk-shaped face contacted the piece ofpaper. The second disk served to maintain the axis of the plunger rod inalignment with the axis of the cylindrical sample holder. Eachplexifilamentary strand sample was crushed by placing a 2 lb (0.91 kg)weight on the plunger rod. The crush height (mm) was obtained bymeasuring the height of the sample from the bottom of the cylindricalsample holder to the bottom of the crusher. The plunger and weight wereremoved from the sample after approximately 2 minutes, leaving the pieceof paper in place to facilitate measurement of the restored height ofthe sample. Each sample was allowed to recover approximately 2 minutesand the restored height (mm) of the sample was obtained by measuring theheight of the paper from the center of each of the four sides of thesample holder and averaging the measurements. The crush value (mm/g) iscalculated by subtracting the average crush height from the averagerestored height and dividing by the average of the weights of thesamples. The crush value is a measure of how much the sample recoversits original size after being crushed, with higher values indicatinggreater recovery of original sample height.

The present invention will be described in more detail in the followingexamples.

EXAMPLES Example 1

Example 1 represents an acoustically absorbing composite of the presentinvention. The staple flash spun plexifilamentary fibers of theacoustically absorbing composite were made by using the flash spinningtechnology as disclosed in U.S. Pat. No. 7,744,989 to Marin.Plexifilamentary fibers were flash spun at a temperature of 205° C. froma 20 weight percent concentration of high density polyethylene having amelt index of 0.7 g/10 min (measured according to ASTM D-1238 at 190° C.and 2.16 kg load) in a spin agent of 60 weight percent normal pentaneand 40 weight percent cyclopentane. The plexifilamentary fibers wereunbonded. The plexifilamentary fibers were cut to a length of about 2.5cm to make the staple flash spun plexifilamentary fibers. The stapleflash spun plexifilamentary fibers had a surface area of 8 m2/g and acrush value of 1 mm/g. A blend composed of 70% of the staple flash spunplexifilamentary fibers were then mixed with staple 15% polyester fiberswith a cut length of about 2 cm and 15% of a low melting bicomponentsheath/core binder fiber of a polyester copolymer as the sheath andpolyethylene terephthalate as the core. The staple mixture is fed to acarding machine. The carding process splits the larger diameterplexifilamentary fibers into microfibers and further produces a fibrousstructure or carded web. The carded web is fed onto a conveyor belt orapron to a crosslapper, where lapper aprons crosslap the carded web 8times by means of a traversing a carrier such as an intermediate apronin a reciprocating motion, to produce a acoustically absorbing batt offibers that are oriented primarily in the transverse direction. Anonwoven facer, Tyvek® Homewrap™ (available from the DuPont Company,Wilmington, Del.) was then adhered to the acoustically absorbing batt bya spray on adhesive of 77 Multi-purpose (available from 3M, St. Paul,Minn.). The resulting acoustically absorbing composite had a basisweight of 322.92 g/m2, a thickness of 0.01905 m, a bulk density of 16951g/m3 and an acoustic absorption maximum at 828 hz. This would be aneffective low frequency sound absorber for buildings, appliances,interior passenger compartments and exterior components of automotivevehicles.

Example 2

The acoustically absorbing batt of Example 2 is produced by the sameprocess as Example 1 except the traversing carrier of the crosslapperplaced 18 laps on the batt instead of 8. A nonwoven facer, Tyvek®Homewrap™ (available from the DuPont Company, Wilmington, Del.) was thenadhered to the acoustically absorbing batt by a spray on adhesive of 77Multi-purpose (available from 3M, St. Paul, Minn.). The resultingacoustically absorbing composite had a basis weight of 352.29 g/m2, athickness of 0.0220 m, a bulk density of 16013 g/m3 and an acousticabsorption maximum at 654 hz. This would be an effective low frequencysound absorber for buildings, appliances, interior passengercompartments and exterior components of automotive vehicles.

Example 3

Example 3 represents an acoustically absorbing composite of the presentinvention. The staple flash spun plexifilamentary fibers of theacoustically absorbing composite were made by using the flash spinningtechnology as disclosed in U.S. Pat. No. 7,744,989 to Marin.Plexifilamentary fibers were flash spun at a temperature of 205° C. froma 20 weight percent concentration of high density polyethylene having amelt index of 0.7 g/10 min (measured according to ASTM D-1238 at 190° C.and 2.16 kg load) in a spin agent of 60 weight percent normal pentaneand 40 weight percent cyclopentane. The plexifilamentary fibers wereunbonded. The plexifilamentary fibers were cut to a length of about 2.5cm to make the staple flash spun plexifilamentary fibers. The stapleflash spun plexifilamentary fibers had a surface area of 8 m2/g and acrush value of 1 mm/g. A blend composed of 40% of the staple flash spunplexifilamentary fibers were then mixed with staple 45% polyester fiberswith a cut length of about 2 cm and 15% of a low melting bicomponentsheath/core binder fiber of a polyester copolymer as the sheath andpolyethylene terephthalate as the core. The staple mixture is fed to acarding machine. The carding process splits the larger diameterplexifilamentary fibers into microfibers and further produces a fibrousstructure or carded web. The carded web is fed onto a conveyor belt orapron to a crosslapper, where lapper aprons crosslap the carded web 8times by means of a traversing a carrier such as an intermediate apronin a reciprocating motion, to produce a acoustically absorbing batt offibers that are oriented primarily in the transverse direction. Anonwoven facer, Tyvek® Homewrap™ (available from the DuPont Company,Wilmington, Del.) was then adhered to the acoustically absorbing batt bya spray on adhesive of 77 Multi-purpose (available from 3M, St. Paul,Minn.). The resulting acoustically absorbing composite had a basisweight of 304.54 g/m2, a thickness of 0.0220 m, a bulk density of 15986g/m3 and an acoustic absorption maximum at 1124 hz. This would be aneffective low frequency sound absorber for buildings, appliances,interior passenger compartments and exterior components of automotivevehicles.

Example 4

The acoustically absorbing batt of Example 4 is produced by the sameprocess as Example 3 except the traversing carrier of the crosslapperplaced 18 laps on the batt instead of 8. A nonwoven facer, Tyvek®Homewrap™ (available from the DuPont Company, Wilmington, Del.) was thenadhered to the acoustically absorbing batt by a spray on adhesive of 77Multi-purpose (available from 3M, St. Paul, Minn.). The resultingacoustically absorbing composite had a basis weight of 342.94 g/m2, athickness of 0.0220 m, a bulk density of 16013 g/m3 and an acousticabsorption maximum at 960 hz. This would be an effective low frequencysound absorber for buildings, appliances, interior passengercompartments and exterior components of automotive vehicles.

What is claimed is:
 1. A tunable acoustically absorbing articlecomprising: (a) a batt of acoustically absorbing material having twomajor surfaces comprising: (i) 10 to 70% by weight staple flash spunplexifilamentary fibers or staple melt spun fibrillated fibers, (ii) 10to 70% by weight staple fibers, (iii) 5 to 30% by weight binding agent,(iv) carded and crosslapped; and (b) a facer adhered said batt on atleast one major surface.
 2. The tunable acoustically absorbing articleof claim 1 that is crosslapped at least 4 laps.
 3. The tunableacoustically absorbing article of claim 1 that is crosslapped at least 8laps.
 4. The tunable acoustically absorbing article of claim 1 where thestaple flash spun plexifilamentary fibers or staple melt spun fibers areat least 30% by weight.
 5. The tunable acoustically absorbing article ofclaim 4 that is crosslapped at least 4 laps.
 6. The tunable acousticallyabsorbing article of claim 4 that is crosslapped at least 8 laps.
 7. Thetunable acoustically absorbing article of claim 1 where the staple flashspun plexifilamentary fibers or staple melt spun fibers are at least 50%by weight.
 8. The tunable acoustically absorbing article of claim 7 thatis crosslapped at least 4 laps.
 9. The tunable acoustically absorbingarticle of claim 7 that is crosslapped at least 8 laps.